Re: [Ntp] Local time in NTPv5?

[Miroslav Lichvar <[e-mail]>]

On Sat, Jul 30, 2022 at 10:56:07PM -0400, Danny Mayer wrote:
> This makes no sense at all. NTP only knows about UTC. All major operating
> systems store timestamps in UTC. Time-zones are just a display issue.

This is about very simple devices like a large digital clock that you
mount on a wall in an office or warehouse, plug it to the network with
PoE, and expect it to display local time. It may not have any
operating system, or any services accessible from the network. Just a
simple firmware with a DHCP and NTP client.

The NTP server is provided in the option 42 (or 56 for IPv6). This is
well known and widely used.

For the timezone it seems there are three options. The old option 2
(time offset) and more recent options 100 (TZ POSIX string) and 101
(TZ name) from RFC4833. Option 2 provides only the current offset, so
this wouldn't work well with DST changes. The option 101 requires the
client to have an up-to-date TZ database, but the option 100 provides
the current timezone itself as a string, including DST. This should
work well in this use case.

I guess those devices I heard people complaining about didn't support
this option, or maybe they didn't have it documented. It could be an
awareness issue. I didn't know it existed before starting this thread.

If there is no good use case for local time without DHCP, I agree that
it would be better to leave it out of NTPv5.

-- 
Miroslav Lichvar